When i switched to mac (more than 5 years ago) I changed computer, I changed operating system and I changed email client too. In linux and windows I used Mozilla thunderbird and I was satisfied with it, when I switched to Apple Mail.app I didn’t notice any problem so I decided to use it in the last years.
Now I’m thinking about to switch again to Mozilla Thunderbird. In the lastmonths I’m having troubles with Mail.app, it looks don’t like too much IMAP server. I mean .. it worked for years but in the last months I’m having problems with crashing, slowness in general and it is becoming quite frustrating.
I suppose that it’s slow due the huge amount of mail I have (I have an archive with all ‘non spam email’), but I cannot accept to do not use email client because I have many emails!
The switch is not really confortable, I have to migrate all emails from Mail.app to Thunderbird so if I will decide to do it I have to decide with attention.
We will see .. by now I’m trying Thunderbird with my IMAP accounts and we will see how it works :)